Durham, N.C. -- The great apes are the smartest of all nonhuman primates, with orangutans and chimpanzees consistently besting monkeys and lemurs on a variety of intelligence tests, Duke University Medical Center researchers have found.
"It's clear that some species can and do develop enhanced abilities for solving particular problems," said Robert O. Deaner, Ph.D., who led the study as part of his doctoral dissertation. "But our results imply that natural selection may favor a general type of intelligence in some circumstances. We suspect that this was crucial in human evolution."
The study was published online August 1, 2006, in the journal Evolutionary Psychology. Funding was provided by the medical center's Department of Biological Anthropology and Anatomy.
Experts in psychology broadly define intelligence as general problem-solving skills -- "domain-general cognition" in the parlance of the field. This intelligence allows an animal to tackle new and unpredictable situations. Domain-general cognitive ability is separate from domain-specific abilities for solving certain environmental challenges, such as a bird remembering where it cached food.
Intelligence testing of animals has repeatedly revealed that some species perform better than others. This suggests that some animals have better domain-general skills, Deaner said. However, scientists have been hard-pressed to convincingly prove these differences could be attributed to intelligence, he added.
"The trouble is that one species may outperform another in a problem-solving test not because it's smarter, but because one species is poorly suited to that particular testing situation," he said. For example, one species may be more comfortable grabbing a joystick.
Deaner and his colleagues reasoned that they could refute this premise -- that performance differences resulted from particular testing situations -- by demonstrating that some primate species
Contact: Robert Deaner
Duke University Medical Center